Objective: (1) To characterize potential changes in diclofenac pharmacokinetics and renal function in patients with rheumatoid arthritis (RA) treated with diclofenac and cyclosporine; (2) to prospectively collect longitudinal safety data during use of this drug combination.
Methods: Twenty patients with severe, treatment refractory RA were sequentially treated with stable doses of diclofenac (100-200 mg/day) for one month followed by diclofenac combined with cyclosporine (3 mg/kg/day) for one month. Pharmacokinetic profiles of diclofenac were obtained at the end of each treatment period. Combined therapy was continued for an additional 5 months, during which doses of both drugs could be individually titrated and safety data collected.
Results: During co-administration, diclofenac exposure doubled, as shown by an average 104% increase in the area-under-the-curve. Diclofenac half-life was not altered. Serum creatinine was significantly elevated from a baseline value of 0.8 +/- 0.1 mg/dl on diclofenac alone to 1.0 +/- 0.3 mg/dl after one month co-administration with cyclosporine. The magnitude of creatinine elevation was not correlated with that of change in diclofenac exposure, suggesting the pharmacokinetic interaction per se may not additionally contribute to the effect on renal function resulting from this drug combination. During longterm treatment with both medications, prospectively collected safety data indicated that renal function could be stabilized when drug doses were individually titrated in response to serial clinical and laboratory evaluations. The overall pattern of adverse events and laboratory abnormalities in the study population were similar to those reported in patients with RA treated with other nonsteroidal antiinflammatory agents and concomitant cyclosporine.
Conclusion: Diclofenac can be safely combined with cyclosporine in the management of RA when appropriate clinical monitoring and dose titrations are performed. Due to the pharmacokinetic interaction that increases diclofenac systemic exposure, it would be prudent to start combination therapy with diclofenac doses at the lower end of the therapeutic dose range.